ON SELF-STERILITY. 217 
1. It has so far been in no case demonstrated that plants of vigorous 
vegetative reproduction have entirely lost their capacity for sexual 
propagation. 
2. On the other hand, such plants can apparently lose throughout 
entire districts the capacity for forming seeds capable of germination, when 
the flowering individuals are of the same vegetative origin. In fact, how- 
ever, they are only self-sterile in the wider sense, and fertilisation can at 
any time be again effected by rendering possible foreign pollination by 
physiologically separate individuals. 
3. Among perennial plants, which do not propagate themselves by 
rhizomes, bulbils, or other asexual means, self-sterility very often occurs 
with species in which cross-fertilisation appears to be secured. 
4, With plants of asexual propagation it appears to increase with the 
predominance of the asexual reproduction. 
5. In the last two cases named, with viviparous, bulbiferous, &c. 
species, and with perennial plants which do not propagate asexually, there 
may arise races, within the same species, which are self-sterile and 
self-fertile. 
6. By introducing new plant species into our gardens, it is therefore 
‘always to be recommended, even when the species are hermaphrodite, 
homostylic, homogamic, &c., to obtain of each species at least two 
examples of as different origin as possible, or to introduce the seed from 
such. 
